The present invention relates to improved method for producing magnetic recording media, and more particularly relates to an improvement in production of magnetic recording media by anode oxidation of an Al predominant substrate, deposition of ferromagnetic substance in substrate pores and final surface grinding.
For better high density magnetic recording, a magnetic recording layer should preferably be as thin as possible and the gap between the magnetic recording layer and a magnetic head should preferably as small as possible. Since degree of packing of ferromangetic substance is usually uneven in construction of a magnetic recording medium producted by ferromagnetic substance deposition in Al oxidized surface layer pores, grinding is applied to the surface of the magnetic recording medium after the deposition in order to even the length of ferromagnetic substance poles in the pores and obtain a thickness necessary for intended magnetic recording.
The surface roughness (Ra) of the Al substrate is in general adjusted to 0.01 .mu.m or less by grinding or diamond cutting.
As remarked above, the gap between a magnetic recording medium and a magnetic head should preferably as small as possible. More specifically, the gap should be about 1/10 the recording wave length. Thus surface grinding of the Al substrate must have high accuracy.
During anode oxidation, the surface of the Al substrate is marred due to etching by the acid or alkali used for the treatment. Even when the original surface roughness of the Al substrate is 0.01 .mu.m or less, the resultant surface roughness exceeds this value and no intended surface smoothness is obtainable by surface grinding or cutting to be applied after ferromagnetic substance packing.
When surface finishing is effected by cutting, accuracy of the product is swayed by production accuracy of the cutting machine. With current standard of cutting machines, it is difficult to produce high surface smoothness after anode oxidation by mechanical cutting. Machines used for grinding in general have high production accuracy. But, in this case, accuracy of the product is swayed by that of the crude workpiece. In the case of the conventional methods, surface accuracy of the magnetic recording medium is inevitably degraded by the high surface roughness after the anode oxidation. Thus, the gap between magnetic recording media and a magnetic head cannot be minimized as desired from the viewpoint of high recording density.